1. Field of the Invention
The present invention generally relates to copy-protected optical information recording media and methods for manufacturing the same. More specifically, the present invention relates to the manufacture of an optically readable digital storage medium that protects the information stored thereon from being copied using conventional optical medium readers, such as CD and DVD laser readers, but permits reading of the information from the digital storage media by the same readers.
2. Background of the Invention
Optical data storage media (xe2x80x9coptical mediaxe2x80x9d) are media in which data is stored in an optically readable manner. Data on optical media are encoded by optical changes in one or more layers of the media. Optical data media are used to distribute, store and access large volumes of data. Formats of optical medium include read-only formats such as CD-DA (digital audio compact disc), CD-ROM (CD-read-only memory), DVD (digital versatile disc or digital video disc) media, write-once read-many times (WORM) formats such as CD-R (CD-recordable), and DVD-R (DVD-recordable), as well as rewritable formats such as found on magneto-optical (MO) discs, CD-RW (CD-rewriteable), DVD-RAM (DVD-Random Access Media), DVDxe2x88x92RW or DVD+RW (DVD-rewriteable), PD (Phase change Dual disk by Panasonic) and other phase change optical discs. Erasable, or rewritable, optical discs function in a similar manner to magneto-optical (MO) disks and can be rewritten over and over. MO discs are very robust and are geared to business applications, typically in high-capacity disk libraries.
Optical media have grown tremendously in popularity since their first introduction owing in a great deal to their high capacity for storing data as well as their open standards. For example, a commercially available magnetic floppy diskette is only capable of storing 1.44 Mb of data, whereas an optical CD-ROM of approximately the same size can have a capacity in excess of 600 MB. A DVD has a recording density which is significantly greater than a CD. For example, conventional DVD read-only discs currently have a capacity of from 4.7 GB (DVD-5, 1 side/1 layer) to 17.0 GB (DVD-18, 2 sides/2 layers), write-once DVDs a capacity of 3.95 GB (DVD-R, 1 side/1 layer) to 7.90 GB (DVD-R, 2 sides/1 layer) (newer DVD-Rs can hold up to 4.7 GB per side), and conventional rewritable DVDs of from 2.6 GB (DVD-RAM, 1 side/1 layer) to 10.4 GB (MMVF, 2 sides/1 layer). Optical discs have made great strides in replacing cassette tapes and floppy disks in the music and software industries, and significant in-roads in replacing video cassette tapes in the home video industry.
Data is stored on optical media by forming optical deformations or marks at discrete locations in one or more layers of the medium. Such deformations or marks effectuate changes in light reflectivity. To read the data on an optical medium, an optical medium player or reader is used. An optical medium player or reader conventionally shines a small spot of laser light, the xe2x80x9creadoutxe2x80x9d spot, through the disc substrate onto the data layer containing such optical deformations or marks as the medium or laser head rotates.
In conventional xe2x80x9cread-onlyxe2x80x9d type optical media (e.g, xe2x80x9cCD-ROMxe2x80x9d), data is generally stored as a series of xe2x80x9cpitsxe2x80x9d embossed with a plane of xe2x80x9clandsxe2x80x9d. Microscopic pits formed in the surface of the plastic medium are arranged in tracks, conventionally spaced radially from the center hub in a spiral track originating at the medium center hub and ending toward the medium""s outer rim. The pitted side of the medium is coated with a reflectance layer such as a thin layer of aluminum or gold. A lacquer layer is typically coated thereon as a protective layer.
The intensity of the light reflected from a read-only medium""s surface by an optical medium player or reader varies according to the presence or absence of pits along the information track. When the readout spot is over the flat part of the track more light is reflected directly from the disc than when the readout spot is over a pit. A photodetector and other electronics inside the optical medium player translate the signal from the transition points between these pits and lands caused by this variation into the 0s and 1s of the digital code representing the stored information.
A number of types of optical media are available which permit an end-user to record data on the media, such optical media generally are categorized as xe2x80x9cwritablexe2x80x9d or xe2x80x9crecordable,xe2x80x9d or xe2x80x9cre-writable.xe2x80x9d
xe2x80x9cWritablexe2x80x9d or xe2x80x9crecordablexe2x80x9d optical media (e.g., xe2x80x9cCD-Rxe2x80x9d discs) permit an end-user to write data permanently to the medium. Writable media are designed such that laser light in the writer apparatus causes permanent deformations or changes in the optical reflectivity of discrete areas of the data layer(s) of the medium. Numerous writable optical media are known, including those that employ a laser deformable layer in their construct upon which optically-readable areas analogous to the pits and lands found in conventional read-only optical media can be formed (See, e.g., EP-A2-0353391), those that employ a liquid-crystalline material in their data layer(s) such that irradiation with the laser beam causes permanent optical deformations in the data layer (See, e.g., U.S. Pat. No. 6,139,933 which employs such layer between two reflective layers to effect a Fabry-Perot interferometer), and those that utilize a dye that irreversibly changes state when exposed to a high power writing laser diode and maintains such state when read with a low power reading laser (so-called, WORM, write-once-read-many times, optical media).
Rewritable optical media (e.g., xe2x80x9cCD-RWxe2x80x9d, xe2x80x9cDVD-RAMxe2x80x9d, xe2x80x9cDVDxe2x88x92RWxe2x80x9d, xe2x80x9cDVD+RWxe2x80x9d and xe2x80x9cPDxe2x80x9d media) use the laser beam to cause reversible optical deformations or marks in the data layer(s), such that the data layer is capable of being written on, read, erased and rewritten on many times. Several rewritable optical media systems are known.
In one system, an optically-deformable data layer is deformed in discrete areas by the writing laser to form optical changes representative of the data, for example, pits and lands, and erased by uniformly deforming the same optically-deformable data layer, or the portion thereof wherein the data desired to be deleted is found. In another system, a photochromic material layer is used to store the data. In this system, the photochromic material reversibly changes when the material is irradiated by light possessing certain wavelengths. For example, a colorless compound may change its molecular state to a quasi-stable colored state when irradiated by ultraviolet (UV) light, yet be returned to the colorless state upon exposure to visible light. By selectively irradiating the photochromic material layer with the one wavelength to cause an optical change, and then irradiating with the other wavelength to reverse such optical change, one is permitted to write, erase, and re-write data.
Materials that changes color due to a change in crystalline state have been found to be particularly useful in re-writable media. In one system, a material which is dark in the amorphous state, but bright in the crystalline state, is used to record the data. In such system, dark amorphous marks are formed utilizing a short high-power laser pulse that melts the recording material followed by quenching to temperatures below the crystalline temperature. The data formed thereby, can be erased by heating the amorphous state over a long enough period of time between the temperature of crystallization and temperature of melt to regain the crystalline state. Ternary stoichiometric compounds containing Ge, Sb and Te (e.g., Ge1Sb2Te4Ge2Sb2Te5) are in particular known to show a large optical contrast between amorphous and crystalline phase and have acceptable melting temperatures (tcryst=about 150-200xc2x0 C., tmelt=about 600xc2x0 C.). Alloys of such compounds with antimony (Sb), cadmium (Cd) and tin (Sn) have also been employed in rewritable media.
In rewritable optical media control information such as address data, rotation control signal, user information etc. is generally previously recorded on the header field in the form of pre-pits.
Data may also be stored in what are referred to as fluorescent multilayer disks. In fluorescent memory storage, the data is present as local variations of fluorescent substance properties. Typically the substance is illuminated with radiation at excitation wavelength, and the fluorescence signal is registered at a different wavelength. A spectral filter is used to separate the fluorescent signal at the receiver from the noise of the excitation radiation. Data may be stored in a 3-D manner using the fluorescent principle. The two-photon approach is often utilized when the fluorescent medium is to be rewritable. In this approach a fluorescent medium containing photochromic molecules capable of existing in two isomeric forms is used. The first isomeric form is not fluorescent and has absorption bands for UV radiation, and is capable of being transferred into the second isomeric form upon the simultaneous absorption of two long wavelength photons which is capable of exhibiting fluorescence.
Hybrid optical media are also known. For example, xe2x80x9chalf-and-halfxe2x80x9d discs are known wherein one portion of the disc has conventional CD-ROM pits and the other portion of the disc has a groove pressed into the disc with a dye layer thereover to form a CD-R portion. A relatively new hybrid optical media is the CD-ROM (i.e., CD programmable ROM). The CD-PROM medium combines a read-only CD-ROM format with a recordable CD-R format on one medium, but features only a single continuous groove on the medium with the entire medium coated with a dye layer. The geometry of the continuous groove of the CD-PROM medium is modulated so as to look like ROM pits to an optical reader. It also provides no dye transition issues to overcome in manufacturing.
An optical disc medium read by moving a read head generating a radiation beam in a specified path relative to the optical medium. The radiation beam is used to differentiate regions having different optical properties, such different optical properties being used to represent the data, for example, the xe2x80x9conxe2x80x9d logical state being represented by a particular region. The detectable differences are converted into electrical signals, which are then converted to a format that can be conveniently manipulated by a signal processing system. For example, by setting a threshold level of reflectance, transitions between pits and lands may be detected at the point where the signal generated from the reflectance crosses a threshold level. The pits represent a 1 and lands a 0. In this manner, binary information may be read from the medium.
The vast majority of commercially-available software, video, audio, and entertainment pieces available today are recorded in read-only optical format. One reason for this is that data replication onto read-only optical formats is significantly cheaper than data replication onto writable and rewritable optical formats. Another reason is that read-only formats are less problematical from a reading reliability standpoint. For example, some CD readers/players have trouble reading CD-R media, which has a lower reflectivity, and thus requires a higher-powered reading laser, or one that is better xe2x80x9ctunedxe2x80x9d to a specific wavelength.
Data is conventionally written onto pre-fabricated writeable and rewritable medium individually, for example, one disc at a time, using a laser. Data is conventionally stamped onto read-only media by a die moulding (injection moulding) process during the manufacture of the read-only medium. Today many more data-containing optical media can be manufactured by the stamping process than by the laser writing process over a set unit of time, significantly reducing the cost of such stamped read-only optical media for large quantities of optical media. The manufacturing of a stamped medium is also considerably cheaper than in fabricating a fluorescent multi-layer medium.
Interference/reflectivity type optical media comprising a read-only format are typically manufactured following a number of defined steps:
Data to be encoded on the medium is first pre-mastered (formatted) such that data can be converted into a series of laser bursts by a laser which will be directed onto a glass master platter. The glass master platter is conventionally coated with a photoresist such that when the laser beam from the LBR (laser beam recorder) hits the glass master a portion of the photoresist coat is xe2x80x9cburntxe2x80x9d or exposed. After being exposed to the laser beam, it is cured and the photoresist in the unexposed area rinsed off. The resulting glass master is electroplated with a metal, typically Ag or Ni. The electroformed stamper medium thus formed has physical features representing the data. When large numbers of optical media of the disc-type are to be manufactured, the electroformed stamper medium is conventionally called a xe2x80x9cfather discxe2x80x9d. The father disc is typically used to make a mirror image xe2x80x9cmother disc,xe2x80x9d which is used to make a plurality of xe2x80x9cchildren discsxe2x80x9d often referred to as xe2x80x9cstampersxe2x80x9d in the art. Stampers are used to make production quantities of replica discs, each containing the data and tracking information which was recorded on the glass master. If only a few discs are to be replicated (fewer than 10,000) and time or costs are to be conserved, the original xe2x80x9cfatherxe2x80x9d disc might be used as the stamper in the mould rather than creating an entire xe2x80x9cstamper familyxe2x80x9d consisting of a xe2x80x9cfatherxe2x80x9d, xe2x80x9cmotherxe2x80x9d and xe2x80x9cchildrenxe2x80x9d stampers.
The stamper is typically used in conjunction with an injection molder to produce replica media. Commerically-available injection molding machines subject the mold to a large amount of pressure by piston-driven presses, in excess of 20,000 pounds.
In the optical medium moulding process, a resin is forced in through a sprue channel into a cavity within the optical tooling (mold) to form the optical medium substrate. Today most optical discs are made of optical-grade polycarbonate which is kept dry and clean to protect against reaction with moisture or other contaminants which may introduce birefringence and other problems into the disc, and which is injected into the mold in a molten state at a controlled temperature. The format of the grooves or pits are replicated in the substrate by the stamper as the cavity is filled, and compressed against the stamper. After the part has sufficiently cooled, the optical tooling mold is opened and the sprue and product eject are brought forward for ejecting the formed optical medium off of the stamper. The ejected substrate is handed out by a robot arm or gravity feed to the next station in the replication line, with transport time and distance between stations giving the substrate a chance to cool and harden.
The next step after molding in the manufacture of a read-only format is to apply a layer of reflective metal to the data-bearing side of the substrate (the side with the pits and lands). This is generally accomplished by a sputtering process, where the plastic medium is placed in a vacuum chamber with a metal target, and electrons are shot at the target, bouncing individual molecules of the metal onto the medium, which attracts and holds them by static electricity. The sputtered medium is then removed from the sputtering chamber and spin-coated with a polymer, typically a UV-curable lacquer, over the metal to protect the metal layer from wear and corrosion. Spin-coating occurs when the dispenser measures out a quantity of the polymer onto the medium in the spin-coating chamber and the medium is spun rapidly to disperse the polymer evenly over its entire surface.
After spin-coating, the lacquer (when lacquer is used as the coat) is cured by exposing it to UV radiation from a lamp, and the media are visually inspected for reflectivity using a photodiode to ensure sufficient metal was deposited on the substrate in a sufficiently thick layer so as to permit every bit of data to be read accurately. Optical media that fail the visual inspection are loaded onto a reject spindle and later discarded. Those that pass are generally taken to another station for labeling or packaging. Some of the xe2x80x9cpassedxe2x80x9d media may be spot-checked with other testing equipment for quality assurance purposes.
Optical media have greatly reduced the manufacturing costs involved in selling content such as software, video and audio works, and games, due to their small size and the relatively inexpensive amount of resources involved in their production. They have also unfortunately improved the economics of the pirate, and in some media, such as video and audio, have permitted significantly better pirated-copies to be sold to the general public than permitted with other data storage media. Media distributors report the loss of billions of dollars of potential sales due to high quality copies.
Typically, a pirate makes an optical master by extracting logic data from the optical medium, copying it onto a magnetic tape, and setting the tape on a mastering apparatus. Pirates also sometimes use CD or DVD recordable medium duplicator equipment to make copies of a distributed medium, which duplicated copies can be sold directly or used as pre-masters for creating a new glass master for replication. Hundreds of thousands of pirated optical media can be pressed from a single master with no degradation in the quality of the information stored on the optical media. As consumer demand for optical media remains high, and because such medium is easily reproduced at a low cost, counterfeiting has become prevalent.
A variety of copy protection techniques and devices have been proposed in the art to limit the unauthorized copying of optical media. Among these techniques are analog Colorstripe Protection System (CPS), CGMS, Content Scrambling System (CSS) and Digital Copy Protection System (DCPS). Analog CPS (also known as Macrovision) provides a method for protecting videotapes as well as DVDs. The implementation of Analog CPS, however, may require the installation of circuitry in every player used to read the media. Typically, when an optical medium or tape is xe2x80x9cMacrovision Protected,xe2x80x9d the electronic circuit sends a colorburst signal to the composite video and s-video outputs of the player resulting in imperfect copies. Unfortunately, the use of Macrovision may also adversely affect normal playback quality.
With CGMS the media may contain information dictating whether or not the contents of the media can be copied. The device that is being used to copy the media must be equipped to recognize the CGMS signal and also must respect the signal in order to prevent copying. The Content Scrambling System (CSS) provides an encryption technique to that is designed to prevent direct, bit-to-bit copying. Each player that incorporates CSS is provided with one of four hundred keys that allow the player to read the data on the media, but prevents the copying of the keys needed to decrypt the data. However, the CSS algorithm has been broken and has been disseminated over the Internet, allowing unscrupulous copyists to produce copies of encrypted optical media.
The Digital Copy Protection System (DCPS) provides a method whereby devices that are capable of copying digital media may only copy medium that is marked as copyable. Thus, the optical medium itself may be designated as uncopyable. However, for the system to be useful, the copying device must include the software that respects that xe2x80x9cno copyxe2x80x9d designation.
While presently available copy protection techniques make it more difficult to copy data from optical media, such techniques have not been shown to be very effective in preventing large scale manufacture of counterfeit copies. The hardware changes necessary to effectuate many copy protection schemes simply have not been widely accepted. Nor have encryption code protection schemes been found to be fool proof in their reduction of the copying data from optical medium, as data encryption techniques are routinely cracked.
There is a need therefore for a copy-protected optical medium which does not depend entirely on encryption codes or special hardware to prevent the copying of the optical medium. Such optical media should also be easily and economically manufactured given the current strictures of optical medium manufacture. The copy-protected media should also be readable by the large number of existing optical medium readers or players without requiring modifications to those devices.
xe2x80x9cAuthentication Materialxe2x80x9d refers to a material used to authenticate, identify or protect an optical medium. The data recorded on an optical medium, for example, software, video or audio files, are not authentication material.
xe2x80x9cCommunication Systemxe2x80x9d refers to any system or network for transferring digital data from a source to a target.
xe2x80x9cLight-ChangeableMaterialxe2x80x9d: a material that absorbs, reflects, emits or otherwise alters electromagnetic radiation directed at the same. By xe2x80x9clight-changeable compoundxe2x80x9d it is meant to include, without limitation, xe2x80x9clight-sensitivexe2x80x9d, xe2x80x9clight-emissivexe2x80x9d and xe2x80x9clight-absorbingxe2x80x9d compounds, as defined below.
xe2x80x9cLight-Emissive materialxe2x80x9d: a material that emits light in response to excitation with light. Light emission can be a result of phosphorescence, chemiluminescence, or, more preferably, fluorescence. By the term xe2x80x9clight-emissive compounds,xe2x80x9d it is meant to include compounds that have one or more of the following properties: 1) they are a fluorescent, phosphorescent, or luminescent; 2) react, or interact, with components of the sample or the standard or both to yield at least one fluorescent, phosphorescent, or luminescent compound; or 3) react, or interact, with at least one fluorescent, phosphorescent, or luminescent compound to alter emission at the emission wavelength.
xe2x80x9cLight-Absorbing Compoundsxe2x80x9d: compounds that absorb light in response to irradiation with light. Light absorption can be the result of any chemical reaction known to those of skill in the art.
xe2x80x9cLight-Sensitive Materialxe2x80x9d: a material capable of being activated so as to change in a physically measurable manner, upon exposure to one or more wavelengths of light.
xe2x80x9cNon-Destructive Security Dyexe2x80x9d refers to a security dye that does not render media permanently unreadable.
xe2x80x9cOpacity-Resistant Light-Sensitive Materialxe2x80x9d: a material capable of being activated so as to change in a physically measurable manner, other than in opacity, upon exposure to one or more wavelengths of light. A opacity-resistant light-sensitive material may be said to be reversible when the activated change returns to the initial state due to the passage of time or change in ambient conditions.
xe2x80x9cOptical mediumxe2x80x9d: a medium of any geometric shape (not necessarily circular) that is capable of storing digital data that may be read by an optical reader.
xe2x80x9cRecording Dyexe2x80x9d refers to a chemical compound that may be used with an optical recording medium to record digital data on the recording layer.
xe2x80x9cReaderxe2x80x9d: any device capable of detecting data that has been recorded on an optical medium. By the term xe2x80x9creaderxe2x80x9d it is meant to include, without limitation, a player. Examples are CD and DVD readers.
xe2x80x9cRead-only Optical Mediumxe2x80x9d: an optical medium that has digital data stored in a series of pits and lands.
xe2x80x9cRecording Layerxe2x80x9d: a section of an optical medium where the data is recorded for reading, playing or uploading to a computer. Such data may include software programs, software data, audio files and video files.
xe2x80x9cRegistration Markxe2x80x9d: a physical and/or optical mark used to allow precise alignment between one substrate and another substrate such that when the registration marks are aligned, the corresponding positions on each substrate are known. For example, when two medium are juxtaposed against one another such that their registration marks are aligned, the point on one substrate corresponding to a physical and/or optical deformation on the other substrate is known.
xe2x80x9cRe-readxe2x80x9d: reading a portion of the data recorded on a medium after it has been initially read.
xe2x80x9cReversible Light-Sensitive Materialxe2x80x9d: a light-sensitive material is said to be reversible when the activated change returns to the initial state due to the passage of time or change in ambient conditions.
xe2x80x9cSecurity Dyexe2x80x9d refers to a compound that may provide or alter a signal to protect the data on a storage medium.
xe2x80x9cTemporary Materialxe2x80x9d refers to material that is detectable for a limited amount of time or a limited number of readings.
The present invention provides an optical medium, and a method of manufacturer thereof, that provides copy protection by incorporating a light-changeable compound in or on the optical medium at discrete positions (loci) such that it provides for altering of the digital data output from a section of the recording layer in a predictable manner. Such optical medium permits the data to be read without requiring alteration to the hardware, firmware or software used in optical media readers while preventing reproduction of the medium. The optical media of the present invention provide producers and distributors of digital data with a data distribution medium that prevents reproducing of their digital data, for example, software, audio and video. The present invention particularly relates to read-only optical medium including, but not limited to CD, CD-ROM, DVD, DVD-5, DVD-9, DVD-10, DVD-18 and DVD-ROM, where optical deformations representing the data are introduced permanently into at least a portion of the optical medium prior to distribution to an end-user. As would be understood by one of ordinary skill in the art, however, the present invention may also be used with writable and re-writable optical media such as CD-R and DVD-R.
The present inventors have discovered a method for altering and/or augmenting the optically-read data stored on an optical medium in a manner that does not prevent the underlying data from being read by a conventional optical medium reader, but prevents the production of a useable optical medium copy using such conventional optical medium readers. The present inventors have found that by selectively placing certain reversible light-changeable materials, and in particular light-emissive materials, at discrete positions on an optical medium, that a conventional optical reader can be made at the first pass of such positions to read the data represented by the optical deformations correctly, but on a second pass read the data differently due to the activation of the reversible light-changeable material. That is, the passing light of the reader may be used to influence the compound and change its properties so that upon re-reading, the data signal that is received by the detector is different from that which was received upon initial sampling. For example, the light-changeable compound may become reflective within a timeframe that provides for reflectance of the light beam upon resampling. Alternatively, the light-changeable material may provide for delayed emission or absorbance of light, thereby altering the signal either positively or negatively.
As most optical media readers and players are pre-programmed to re-sample data areas of the recording layer to assure correct copying, optical medium of an embodiment of the present invention will fail to copy, as a data string read from the recording layer will vary according to whether the light-changeable material is activated upon sampling. That is, re-sampling of a data area in proximity to the light-changeable material may result in a different data read than when the data was initially read. Even if a copy can be made, that copy will be invalid if a program on the optical medium requires two different reads to access data on the optical medium. That is, the copy will be invalid since it will only represent one of two possible states at that data locus.
The present invention provides for specific optical media designs, and methods for manufacturing such designs, that incorporate light-changeable materials in a manner that selectively changes the data read-out of the recording layer of an optical medium upon re-sampling of those portions of the recording layer in proximity to the light-changeable material foci. In particular, there is provided optical medium designs that may be easily and economically produced without significantly altering the injection molding manufacturing process of read-only optical media (as set forth above).
In a first embodiment of the present invention there is provided an optical medium having light-changeable material selectively imprinted or placed on the non-impressed (i.e., non-stamped) side of the recording layer of an optical medium. Such medium comprises a first substrate having two major surfaces, a data track disposed along one major surface of the first substrate, and a light-changeable compound disposed on the other major surface of the first substrate cooperating with the data track to alter the data upon excitation with a suitable light stimulus (e.g., a particular wavelength). Such optical medium further preferably comprises a second substrate, preferably of similar optical properties (preferably of the same material), affixedly attached to the surface of the substrate where the light-changeable compound is disposed.
A first embodiment optical medium of the present invention may be produced by disposing the light-changeable material onto the non-impressed side of the substrate after the substrate has been stamped and sufficiently cooled, and after the optical tooling mould is opened (but before the sprue and product eject are brought forward for ejecting the formed optical medium off of the stamper). As would be understood by one of ordinary skill in the art such manufacturing technique permits precise registration of the light-changeable material with the data impressions on the other surface of the substrate. Preferably the light-changeable material is covered by a second substrate of similar (or identical) optical properties to protect the light-changeable material from its ambient environment. Such second substrate may be affixed to the first substrate either before or after the sputtering step used to cover the stamped surface of the first substrate. Either or both of the first and second substrates may be spin-coated with an adhesive agent prior to formation of such optical medium such that the layers may be affixedly attached. Alternatively, the light-changeable material may be coated with a polymer, as by spin-coating. For example, an optically-pure lacquer may be used to coat the light-changeable materials.
In a second embodiment of the present invention, there is provided an optical medium comprising a first substrate layer having a first major surface and a second major surface, said first major surface of said first substrate layer having light-changeable material thereon, and either of said first or second major surface of said first substrate layer, or both, having a registration mark thereon; a second substrate layer having a first major surface and a second major surface, said first major surface of said second substrate layer having information pits thereon, and either of said first or second major surface of said second substrate, or both, having a registration mark thereon, said second major surface of said second substrate being disposed along said first major surface of said first substrate layer such that the registration marks of said first and second substrates are aligned; a metal reflector layer, said metal reflector layer being disposed along said first major surface of said second substrate layer; a first overcoat layer being disposed along said metal reflector layer, and optionally a second overcoat layer being disposed along said second major surface of said first substrate layer.
A second embodiment optical medium may be produced by obtaining a first substrate having a first major surface and a second major surface and a registration mark on either of said first or second major surface, or both; imprinting in discrete positions on said first major surface of said first substrate layer light-changeable material; obtaining a second substrate having a first major surface and a second major surface, and a registration mark on either of said first or second major surface, or both, said first major surface of said second substrate layer having information pits thereon; disposing said second major surface of said second substrate along said first major surface of said first substrate such that the registration marks on said first and second substrate are aligned and affixing said second major surface of said second substrate to said first major surface of said first substrate; metalizing said first major surface of said second substrate layer having said information pits; disposing a first overcoat layer along said metalized surface; and optionally disposing a second overcoat layer along said second major surface of said first substrate layer. As would be understood by one of ordinary skill in the art, the registration marks need not be on the actual surface of a substrate, but need to be detectable. By xe2x80x9ca surface having a detectable registration markxe2x80x9d it is meant that a registration mark is detectable therethrough or thereon.
In a third embodiment of the present invention, there is provided an optical medium comprising a substrate having material(s) capable of reacting with one another, or being activated, such that they form a light-changeable material(s) upon exposure to a particular light source of defined energy, such material being coated on the non-impressed (i.e., non-stamped) side of the recording layer of an optical medium. Such optical medium comprises a first substrate, a data track disposed along one surface of the first substrate, and the material(s) capable of being activated to form a light-changeable material(s) upon exposure to a particular light source (of defined energy) coated on the non-embossed surface of the first substrate. For example, a laser may catalyze crosslinking of certain inactive material(s) to form light-changeable compounds, such as a light-emissive material. In this embodiment, the coated material is activated in discrete areas using the appropriate light source (and energy) so as to form a light-changeable material at discrete points which will cooperate by their positioning with respect to the data track to alter the data upon excitation with a suitable light stimulus (e.g., a particular wavelength). This selective activation of various portions of the first substrate to form a light-changeable compound may be performed in a manner similar to that used to write data to a CD-R disc. Such optical medium further preferably comprises a second substrate, preferably of similar optical properties (preferably of the same material), affixedly attached to surface of the substrate where the formed light-changeable compounds are disposed. In an alternative to such embodiment, the material coated on the non-embossed (i.e., non-stamped) side of the recording layer of an optical medium may be light-changeable material that may be selectively deactivated using a laser of particular wavelength and strength. In such case selective activation in the appropriate data spots can be caused by deactivating those portions of the coat which one does not wish to have light-changeable properties.
In a fourth embodiment of the present invention there is provided an optical medium comprising a substrate having two major surfaces, one major surface of the substrate having a data track disposed thereon, and a cohesive layer disposed above such data track, the cohesive layer containing light-changeable material cooperating with data track so as to alter the read of the data stored therein upon excitation with a suitable light stimulus (i.e., activation of the light-changeable material). A preferred optical medium of such embodiment comprises a first molded layer having a data track disposed thereon, a first polymeric layer covering the data track, second polymeric layer comprising the light-changeable material, and a third polymeric layer covering the second polymeric layer. The first polymeric layer may comprise a dielectric layer. The first and and second polymeric layers are preferably less than 3 nm in thickness.
In a fifth embodiment, there is provided copy protection in that the optical optical medium itself has code that instructs the optical reader to re-sample a data area where a light-changeable material is found (or where the light-changeable material affects the read), and to fail to permit the access to the data if upon re-reading the data area, that data elicited is the same as upon initial sampling. In another embodiment, the light-changeable compound must be located at a particular locus for the optical media in operate. For example, software may be included on the optical medium to direct the optical reader to alter its focal length such that the light-changeable material in a plane different from the optical data is detected and access to the optical data permitted only if such light-changeable material is detected.
Yet in a sixth embodiment of the present invention, an optical medium having light-changeable material is formed by selectively placing the light-changeable material into a pit or onto a land of a standard optical medium using microinjection techniques, well known in the art, prior to the metalizing step.
And yet in a seventh embodiment of the present invention, an optical medium having a adhesive material comprising the light-changeable material, said adhesive material being adhered to one or more layer or surfaces of the medium is disclosed. For example, light-changeable material may be placed in a label, or in a optically clear material on a layer or surface of the medium such that the light-changeable material is positioned in the manner desired.